* {
    margin: 0;
    padding: 0;
}

html,
body {
    width: 100%;
    height: 100%;
    background: black;
}

#blood {
    width: 300px;
    height: 30px;
    /* border-radius: 25%; */
    border: 5px solid blue;
    position: relative;
    z-index: 9;
    top: 5px;
    left: 5px;
}

#blood .number {
    height: 100%;
    z-index: 1;
    background: red;
}